The present invention relates to a wafer carrier used in a semiconductor device fabrication system. Particularly, it relates to a compact wafer carrier used in a semiconductor fabrication process, always sending a high class clean air laminated stream directed to the wafers stored thereinside.
In line with the increase in the integration density of semiconductor devices, such as LSIs, the circuit pattern sizes of the semiconductor devices continue to decrease down to submicron sizes. Accordingly, particulate contamination caused by particles and chemicals contained in the fabricating environment, leads to the degradation of the reliability of the fabrication yields of the semiconductor devices. The particulate contamination control of the fabricating environment, therefore, is essential to the fabrication process of the semiconductor device. In order to secure clean fabrication environment, the fabrication processes are generally performed in clean rooms, employing clean benches for work stations of the improtant processes.
As well known, during major part of the earlier fabrication stages of the semiconductor devices, the processes are performed with works which are in the form of semiconductor wafers (hereinafter, referred to as simply `wafers`). Thereby, a plurality of the wafers, are loaded in a wafer carrier, carried from a work station to the next work station, and unloaded from the wafer carrier to be subject to the next fabrication processes. In several cases, the wafers which are loaded in the wafer carrier, are stored temporarily, for example, in a closed clean box prepared in the relevant working area, for waiting for the next fabrication step.
In some fabrication processes, such as water rinsing and wet chemical etching, the wafers are processed without being unloaded from the wafer carrier, which is utilized as a holding jig of the wafers. In all cases, it is substantially important to protect the wafers from the particulate contamination.
The major source of the particulate contamination in the air is personnel. In fact, if a clean room is continuously monitored for particulate contamination, the monitor record clearly shows the extremely low levels of the particulate contamination that occurs between shifts, and the rapid rise in particle counts that occur as personnel occupy the room. Particularly, when the wafers are carried by an operator employing a prior art wafer carrier, or when the wafers are loaded or unloaded from the wafer carrier manually at a work station, the wafers are exposed to a serious particulate contamination because a human body is in the proximity of the wafers, and the prior art wafer carrier is usually of an open type.
FIG. 1 is a perspective view of an example of the prior art wafer carriers, illustrating the structural configuration thereof. The wafer carrier 6 comprises side plates 1a and 1bwhich stand facing to each other. A plurality of horizontal and spaced gooves 2a and 2b are respectively formed on the inner surfaces of the side plates 1a and 1b. The grooves 2a, or 2b, are respectively in parallel with each other, being spaced from each other by a predetermined distance such as 2 to 5 mm. A pair of a groove 2a and a groove 2b which correspond to each other, are aligned with each other, and have an appropriate depth such that both grooves 2a and 2b are adaptable to receive the peripheral edge sides of a wafer 5. Thus, the wafers 5 are held in parallel between the side plates 1a and 1b, keeping the spacing distance therebetween. Both side plates 1a and 1b are connected by a top plate 3 at the upper ends having the same width as that of the side plates 1a and 1b. At the bottom ends of the side plates 1a and 1b, a bottom plate 4 (not shown) having a narrow width, connects both side plates 1a and 1b. With this configuration, the prior art wafer carrier 6 has openings at the front side, the rear side, and the bottom side. These openings allow the loading and unloading of the wafers 5 into and from the wafer carrier 6 without any spatial limitation. However, the intrusion of particles, particularly caused by personnel, into the area immediately surrounding the wafers 5, is inevitable, causing a particulate contamination of the wafers 5.
FIG. 2 is a schematic perspective view of an interface means 30 for unloading the wafers 5 from the wafer carrier 6 by one piece and feeding the wafer 5 onto a processing station, which is currently employed. The means 30 includes an elevator 31 and a belt conveyer 32 which is driven by a motor 33. The height of the belt conveyer 32 is formed substantially thin such that the belt conveyer 32 is easily inserted at the bottom of the stored wafers 5 in the wafer carrier 6 without occupying a large space. The elevator 31 (only a mounting plate thereof is shown in FIG. 2) is controllably moved in the vertically direction (indicated arrow V) and in the horizontal direction (indicated by arrow H), mounting the wafer carrier 6 on the mounting plate. With the interface means 30, by operating the elevator 31, the wafer 5 is placed on the belt conveyer 32, pulled out from the wafer carrier 6, thus is unloaded easily one by one from the bottom. Thereafter, the wafer 5 is transferred by the conveyer 32 and loaded into the work station of the subsequent fabrication process (not shown) which is usually performed in a clean bench. The unloaded wafers 5, therefore, are free from further contamination during the loading and unloading operation from the wafer carrier 6 to a work station. Thereby, if the wafer carrier 6 has a bottom plate 4 with the narrow width covering a partial bottom surface of the storing chamber 7, the unloading operation of the wafer 5 is provided much spatial freedom. However, even though with a bottom plate 4 with the wide width covering the full surface of the bottom, the unloading is also possible. Instead of the above-described interface means 30, various means are available, such as an articulated robot.
On the other hand, chemical interaction with the wafers due to particulate contamination has become a problem in recent semiconductor devices. For example, even after a dry etching process of a wafer using a reactive ion etching (RIE) method, residual radial ions, such as fluoride radicals, are prone to adhere to the surface of the wafer, chemically reacting with the wafer, and providing damages to a circuit pattern formed on the wafer, such as an excess side etching of the relevant pattern. Such chemical particulate contamination is also desirable to be eliminated. The elimination, however, can not be achieved by only statically immersing the wafers in a clean air environment, becasue the adhesion power of the radicals to the surfaces of the wafers is too strong to be released from the surface by stagnant air flow.
There are utilized a wafer carrier of closed type, in which wafers stored in the wafer carrier are protected from the particulate contamination by an air-tight shield case. Although intrusion of the particles contained in the environmental air space can be avoided by the shield, the above-described adhereed chemical radicals, for example, can not be removed from the surfaces of the wafers. In view of the above described chemical aspects of the particulate contamination, the closed type wafer carrier is not effective to eliminate the damage. In addition, the structure including the air-tight shield, provides substantial inconvenience to the loading and unloading of the wafers.
Furthermore, in the fabricating field of semiconductor devices, there are proposed various means for storing wafers, and carrier means for transferring wafers, which are equipped with a clean air supplying means. Several examples will be introduced.
A clean retainer is proposed in Japanese Provisionally Published Patent Application, No.59-39019, published on Mar. 3, 1984, invented by Suzuki et al. The retainer has an air cleaning means including an air filter for supplying clean air therein, which flows from the top side of the retainer to the down side. The wafers stored in a wafer cassette are disposed at the bottom of the retainer. Thus, the wafers may be exposed to clean but stagnant air flow. The retainer is not transportable according to the drawing of the embodiment. A portable clean box is proposed in Japanese Provisionally Published Patent Application, No. 59-172713 published on Sept. 29, 1984, by Nishigatani. The box is compact and portable, and the inside of the box is pressurized by high pressure clean air stored in a small reservoir. No description how to store wafers therein, is found. Further, a clean transferring system is proposed in Japanese Provisionally Published Patent Application, No.60-206017 published on Oct. 17, 1985, invented by Kuno, et al. The system contains a wagon having an air cleaning means to maintain the air space inside the wagon clean. The cleaning means includes a fan, a filter, and a recirculating duct. The wafers are stored on a cassette, and placed on a belt conveyer. The clean air may be stagnant in the space surrounding the wafers which is disposed at the bottom of a storing space. In the above-described clean air vessels having each own air cleaning means, the air flow may stagnate on the surface of the wafers stored, resulting in difficulty in removing particulate contamination originally adhering to the surface of the wafers.